Prior to the present invention a variety of processes have been reported in the literature for the preparation of compacted or compressed materials for use as fuels. For example, U.S. Pat. No. 4,015,951 which issued on Apr. 5, 1977 to R. W. Gunnerman discloses a method for the preparation of pellets, adapted to be burned as fuels in industrial applications. The method, which is directed primarily to wood, is dependent upon the use of materials, which during pelletizing will exude a wax-like material at temperatures of about 325.degree. F. and thereby form a wax-like surface over the pellet. In order to assure that a coating is formed which will impart optimum strength to the pellet, it appears that the particle size of the fibrous material and moisture content are critical.
More recently, U.S. Pat. No. 4,236,897 which issued to I. F. Johnston on Dec. 2, 1980, claims a high, heat value fuel pellet which is comprised of cellulosic material and from about 1 to about 50 percent by weight of a synthetic polymeric thermoplastic material, such as polystyrene. It is indicated in the patent that the term "synthetic thermoplastic materials" excludes naturally occurring thermoplastic materials and naturally occurring cellulosic materials. The advantages of the method are indicated to be resistance of the pellet to crumbling, easy ignition, and high heating value.
However, prior to the present invention the pelletizing of cellulosic materials such as wood wastes for use as a fuel was a very costly operation. This was due to the extremely shortened die life of the pelletizing equipment caused by the excessive abrasiveness of the wood being processed through the die and hence the overall rate of production was low. This problem was a very costly one and to date has largely prevented the preparation of pellets at prices which could be competitive with other compacted fuel systems.
Moreover, prior to the present invention nothing has been reported in the literature of attempts to reduce the abrasiveness of the cellulosic material, such as wood by modification of the cellulose itself, whereby the life of the pelletizing die would be extended, and the production increased.
Accordingly, one or more of the following objects will be achieved by the practice of this invention. It is an object of this invention to provide an improved process for the preparation of fuel pellets. Another object of this invention is to provide a process for the preparation of fuel which is simple and efficient and less costly than known methods. A still further object of the invention is to provide a process for the preparation of fuel pellets which are derived in part from cellulosic materials. Another object is to provide a process which utilizes certain enzymes to modify the cellulose. A further object of this invention is to provide a process wherein the modified cellulose will flow easily into the pelleting press and bond together in the die without the use of excessive mechanical power. A still further object is to provide a process for reducing the abrasive properties of materials such as wood, so that the overall life of the pelletizing die is greatly extended. These and other objects will readily become apparent to those skilled in the art in the light of the teachings herein set forth.